In recent years, widespread use of electric power steering apparatuses (hereinafter referred to as EPSs (Electric Power Steerings)) has being leading to a demand for further improvement of product appeal. Under these circumstances, regarding sustainability of an assist function at the time of a system failure, there has been a demand desiring provision of the function so earnestly that even the function with a time limit imposed thereon would be acceptable. One solution for meeting this demand is an EPS including redundant inverter systems and motor systems and backing up control with use of only one of the systems when a failure has occurred therein, and this EPS also has been starting to be brought to the market.
Japanese Patent Application Public Disclosure No. 2011-142744 (PTL1) discusses one background art in the present technical field. PTL 1 discloses a motor drive apparatus directed to an object of providing a motor drive apparatus capable of controlling a motor appropriately even in a period immediately after starting a motor drive operation. This motor drive apparatus includes a plurality of motor drive parts from first to n-th motor drive parts (n is a natural number equal to or greater than 2), each of the motor drive parts including a winding set corresponding to a plurality of phases and configured to drive a motor and an inverter for supplying a current to the winding set, and a control unit configured to check whether a failure is present with respect to each of the motor drive parts from the first to n-th motor drive parts and control current supply to the winding set through the inverter in each of the motor drive parts. The control unit can execute a series of “m” failure detection processing procedures (m is a natural number) with respect to each of the first to n-th motor drive parts. The control unit is configured to start the current supply to each of the winding sets of the first to n-th motor drive parts after completion of all of the m failure detection processing procedures executed with respect to each of the first to n-th motor drive parts.